BELGRADE — BELGRADE, Yugoslavia -- Fierce fighting in central Bosnia-Herzegovina shattered a new cease-fire yesterday, and the republic's Muslim president cast serious doubt on the chances for a peace agreement that Western mediators have described as close to being completed.

Bosnian President Alija Izetbegovic said in a radio broadcast that he intends to stick by demands for further territorial concessions by Serbian and Croatian nationalists in exchange for an ethnic division of his vanquished state.

European Community mediator Lord Owen and U.N. special envoy Thorvald Stoltenberg had predicted after their latest talks with the Bosnian combatants that all three factions were ready to sign a truce to end the 18-month-old bloodshed at a meeting Tuesday at Sarajevo airport.

"I personally don't see it, and I told Owen that," Mr. Izetbegovic said of the accord the mediators want signed at the airport meeting.

Lord Owen and Mr. Stoltenberg flew from Belgrade to the Adriatic port of Split to discuss the pact with Croatian President Franjo Tudjman after having garnered the support a day earlier of Serbian President Slobodan Milosevic, widely seen as the instigator of the Balkan conflict.

A spokesman for the mediators seemed to back away from their hearty predictions of an imminent settlement, noting that the Sarajevo meeting may be called off if there are signs that the combatants are not ready to agree to peace.

Another sign that the long-sought truce might still be beyond reach was the immediate failure of another cease-fire ordered by Mr. Izetbegovic and Mr. Tudjman to take effect at noon yesterday.

Muslims and Croats battled across a wide swath of central Bosnia, providing fresh proof of the limited authority that political and military leaders have over renegade local factions fighting over territory before the republic's ethnic partitioning.

Military commanders of all three warring parties -- Serbs, Croats and the Muslim-led government -- had met with the U.N. commander for Bosnia a day earlier to pledge their commitment to the cease-fire as a prelude to the truce expected Tuesday.

If the proposed agreement is signed by all three parties and the North Atlantic Treaty Organization makes good on its offer to send in as many as 50,000 enforcement troops, the mediators say, the accord will bring a long-sought end to the deadly Bosnian conflict.

But Croatian Radio and U.N. sources reported that heavy fighting continued unabated in several contested towns. Clashes also were reported to have resumed later in the day in Mostar, which has been devastated by a succession of assaults launched by all three national groups to control one of Bosnia's most important cities.

U.N. spokesman Capt. Yes Frederiksen suggested that some front-line commanders might not know of the cease-fire.

Although Lord Owen and Mr. Stoltenberg have said they have commitments to the expected peace accord from all three Bosnian factions, several disputes over key territories remain.

The framework agreement for Tuesday provides for further talks to determine the exact contours of the ethnic division that will create three independent mini-states out of the current Bosnia.

Control of Mostar and an arc of ethnically tense towns and villages in central Bosnia are among the territorial disputes yet to be settled and likely to fuel further fighting.

Tuesday's meeting, if it takes place, would be the first time Bosnia's rival leaders have met since peace talks in Geneva collapsed nearly three weeks ago when Mr. Izetbegovic insisted that the Muslim state have access to the Adriatic Sea to be economically viable.